Louvered stack for hot air heater



April 1959 R. H. HUNTER ET AL 2,883,979

LOUVERED STACK FOR HOT AIR HEATER Filed Jan. 2. 1958 /NVENT0 Robe/z H Hur'nel am-J Harris W 5 m Z71 ATTORNE Y5 United States Patent LOUVERED STACK FOR nor AIR HEATER Robert H. Hunter, Gates Mills, and Harris W. Smith, Bainbridge, Ohio; said Smith assignor to said Hunter Application January 2, 1953, Serial No. 706,642

11 Claims. (Cl. 126-90) This invention relates to air heaters of the thermosiphon type wherein hot gases from a fluid fuel burner induce convectively the flow of air to be heated through a casing enclosing the burner. The burner gases and heated air are commingled and issue together from the top of the heater for circulation in the space to be heated. More particularly the invention is concerned with the structure and arrangement of the internal baffling of the heater casing to reduce cost, to provide improved combustion characteristics in the burner, more complete and efficient commingling of the burner gases and the air induced to flow through the casing, and to improve generally the thermo siphon action.

One of the principal objects of the invention is to provide an air heater wherein a casing having top and bottom openings is provided with an internal bafliing assembly which divides the air space within the easing into an internal flue passage and a surrounding air chamber with a spreader extending vertically through the center of the flue passage causing the flame and hot gases entering the flue passage through the bottom opening of the stack to travel upwardly primarily in close proximity to the inside surfaces of the stack. As a specialized feature the invention contemplates forming the sheet metal stack with a multiplicity of openings preferably in the form of horizontal louvers through which air rising in the air chamber passes through the stack and into the flue passage.

. Another object is to provide such a heater in which the stack and the baflie each comprises a pair of identical sheet metal elements readily formed by simple cutting and bending operations and easily and quickly assembled together into tubular form.

Another object is to provide stack and bafile assemblies for such a heater in which sheet metal elements are attached together by integral flanges which constitute spacers locating the baflie assembly in the stack and the stack assembly in the heater easing.

Other objects and advantages relating to novel structural arrangements and combinations of parts elfecting simplicity and economy in construction are apparent in the following detailed description of a preferred embodiment representing the best known mode of practising the invention. This description is made in connection with the accompanying drawings forming a part of the specification.

In the drawings:

Fig. 1 is a front elevational view partly in section and with parts broken away and removed showing the heater of the present invention;

Fig. 2 is a vertical section through the heater of Fig. 1 with parts of the baffle assembly broken away and removed and other parts shown in section to reveal the internal structure;

ice

3 is a top view of the heater; and Fig. 4 is a sectional detail of the baflle assembly, this v1ew being taken substantially along the line 4--4 of Fig. 3, the casing being omitted.

The present heater comprises a main or outer casing 1 which, for convenience in manufacture and assembly, is of rectangular cross-section. It may be a single piece of sheet metal such as customarily used in hot air furnaces, bent to the desired shape or, as shown, it may comprise spaced parallel front and rear panels 2, 3 and spaced parallel left and right side panels 4, 5 of suitable sheet metal such as cold rolled steel of about 20 gauge. The panels of the casing, when separately formed, are suitably secured together along the four vertical edge corners as by flanges 6 integrally formed on the edges of the front and rear panels and welded or bolted to the margins of the side panels which they overlap. Suitable means, such as wall attachment brackets on the casing or an open ped estal or closed cabinet base for floor support, is proved for mounting the heater as a removable unit in the cargo space of a truck or trailer so as to permit convective flow of air upwardly through the casing interior. The casing thus provides an internal air space and has bottom and top openings 12, 13 through which the air respectively enters and leaves by thermosiphon action induced by heat from a suitable fluid fuel burner 7. This burner, which receives combustion supporting oxygen from the surrounding air, is supported in the bottom part of the casing air space by suitable means such as cross member 8 having" downturned ends spot welded to casing side panels 2, 3. Fuel, such as propane gas, is supplied under pressure to the burner 7 through a conduit 9 under the control of a? suitable valve or valves and, if desired, governed by conventional thermostatic controls.

In the air space of the casing above the burner 7 is a baflie system or assembly, comprising a stack assembly 10 and a spreader assembly 11, which regulates the flow.

of air and the hot gases from the burner 7. The stack assembly comprises a pair of identical elements 14, 15

formed of a suitable heat resistant fiat sheet metal such as stainless steel or low carbon aluminized steel of about 24 gauge cut and bent along straight lines to the shape of a tapered tube of rectangular section as illustrated in the drawings. Each of the two stack elements has planar panel portions 16, 17 angularly disposed and integrally joined along an edge corner 18. Along its side panel 16 each of the stack elements 14,

15 is formed with an integral angularly disposed flange.

19 disposed flatwise against the marginal portion of the panel 17 of the companion element and secured thereto as by spot-welding 21 to hold the stack elements together.

The stack 10 is of tubular structure and of rectangular,

cross-section. The panels 16, 17 are tapered, with their widest ends uppermost in the casing 1. The side panels 16 at their upper ends are of substantially the same width as the corresponding dimension of the casing 1 so that upperedges 20 of the front and rear panels 17 are disposed against the inside surfaces of the front and rear casing panels 2, 3. The upper ends of the front and rear panel elements 17 are, however, of less width than the corre-'.

gressively decreases in cross section upwardly, can flow,

aeeenrs 33 freely into upper mixing chamber-portion 26 (Pig. 2) of the casing and out the top opening 13.

The downwardly converging stack is formed at its lower end with a flared entrance opening tapered in cross section that receives the upwardly projecting discharge end of the combustion tube of the burner 7. This flared entrance may be provided by a separate member secured to the lower end of the stack or, as shown, by bending outwardly flaps or bottom end portions 28, 29 of the planar panels 16, 17 of the stack elements 14, 15, the bending being done along horizontal lines 3%. A venturi throat 56 in the plane of the horizontal bends 30 is provided by the flaps 28, 29 and the upwardly diverging panels of the stack and has the eflect of producing an effective and eflicient flow of air outwardly into the interior of the stack around the burner 7.

'Extending downwardly into the interior of the stack 10 from the large open upper end of the latter, the spreader assembly 11 divides the rising hot gases to flow through a plurality of relatively narrow passages. The main part or body of the spreader comprises a pair of identical sheet metal members 32, 33 formed of heat resistant metal such as the 24 gauge stainless steel or aluminized steel of which the stack 10 is fabricated. Each of the spreader members has planar panels 34, 35 respectively disposed in spaced generally parallel relation to the panels 16, 17 of the stack elements 14, and providing air passages 36, 37.

The panels 34, 35 of each of the spreader members are angularly disposed relative to one another and integrally joined along adjacent edges, forming corner bends 38. Along their other edges the spreader member panels are formed with integral angularly disposed and outwardly protruding flanges 40, the flanges of one spreader member being disposed flatwise against the flanges of the other spreader member and secured as by spot welding indicated at 41.

At the lower end of the spreader 11 the panels 35 of flae members 32, 33 have integral flange portions 43 bent inwardly to overlie one another as indicated in Fig. 4. The relative thickness of the metal is exaggerated to show the construction. The spreader 11 terminates in a flame interceptor 4-5 in the form of an inverted foursided pyramid made by bending a single piece of sheet metal to the desired shape, or, as shown, by welding together along their converging edges four pieces 39 of sheet metal each having an acutely angled integral flap or flange portion 48. The interceptor pyramid is made of metal of the stainless or aluminized steel type, preferably of somewhat heavier gauge than that employed in the spreader panel members 32 and 33 since the flame interceptor 4,5 is disposed directly in the path of the flame or torch blast issuing from the burner 7.

Each of the four planar side pieces comprising the flame interceptor 45 is triangular in shape and has an integral flap 47 bent inwardly and disposed flatwise against and in overlapping relation to the corresponding flaps of the other side pieces. These flaps collectively comprise a rectangular attaching element of the pyramidal flame interceptor, such element being disposed horizontally and flatwise against the underside of the overlapped flange portions 43 on the lower ends of the spreader members 32, 33. Bolts 47 extending through aligned apertures in the spreader member flange portions 43 and the flaps of the flame interceptor 45 hold the parts together, the flame interceptor being thus detachably mounted for easy replacement if necessary. In original fabrication the four pieces of sheet metal comprising the flame interceptor 45 are assembled on the bolts 47 preliminary to the welding together of their edges.

Thus the torch flame, directed against tip end 46 of the flame interceptor 45 and the air mixed with the flame are divided and deflected laterally by the four sides of the flame interceptor to flow upwardly in the general e} shape of a hollow column of rectangular-section through the four air passages 36, 37 on the four sides of the spreader assembly 11 and between the latter and the panels 16, 17 of the stack assembly 10.

In manufacturing the present heater, the several components are conveniently built separately as sub-assemblies and then brought together in a final unit assembly. Thus, the casing ll, comprising the panels 2-5, is assembled separately from the stack assembly 10 and the spreader assembly ll. Likewise, the stack assembly is put together independently of the spreader assembly 11. The completed spreader assembly 11, including the pyramidal flame interceptor .5, is lowered into the stack assembly 15} in telescopic relation through the top end opening 13 to the position shown to advantage in Fig. 4. The limit of movement is determined by engagement of the edges of the spreader assembly flanges 40 in the corners 38 of the stack assembly 10. A transverse rod 50 received through aligned holes in the stack panels 16 and the spreader panels 34 at the large or upper end of the assembly locks the sub-assemblies together and prevents the spreader assembly from moving out of the stack assembly should the heater be upended. Cotter pins 459 through transverse holes in the ends of the locking pin 50 hold the latter captive in assembled position.

The stack assembly 10 and the interfitted spreader assembly 11 held together by the locking pin 50 are inserted or lowered as a unit into the interior of the casing 1 through the upper end opening 13 of the casing. The inserted unit is located and secured in predetermined position by suitable fasteners such as bolts or sheet metal screws 53 received through pro-punched holes in the front and rear casing panels 2, 3 and the stack panels 17. A wall tie or bracket 55 connects the lower end of the stack assembly to the rear wall panel 3 of the casing to locate the bottom entrance opening or throat 56 of the stack assembly in predetermined relation centered over and about the upwardly directed discharge end of the burner 7. The bracket 55 has integral angularly disposed end flanges disposed flatwise against the stack and easing panels and secured by suitable fasteners 57 such as sheet metal screws and bolts.

One of the casing panels is formed with an opening 59 on the same level as the burner 7 for access to the latter to ignite the flame and in servicing the heater. The opening 50 is normally closed by a door 60 held in place by hinges and screws, not shown. An access hold 61 in one of the stack panels at the level of the burner discharge end permits an igniter to be inserted horizontally into the stack interior, this hole normally being closed by a gravity gate 66 suspended on a pin 67 fast in the stack panel above the hole.

Each of the panels 16, 17 of the stack assembly 10 is formed with a series of horizontal louvers 62. These louvers are made as by a stamping operation without the removal of any metal. The metal is formed with a series of uniformly spaced horizontal slits, the metal above each slit being pressed outwardly to overhang the metal below the slit so that the louver openings are directed downwardly to face the air rising or flowing upwardly inthe chamber surrounding the stack.

In operation the torch flame issuing from the burner 7 blasts upwardly through the lower portion 64 of the stack assembly, drawing air into the stack through the minimum area entrance opening 56; the entering air is directed and guided by the flared or tapered opening provided by the angularly disposed bottom flaps 28, 29.

The indrawn air mixes with the flame and hot gases from the burner 7 in the lower chamber portion 64, the walls of this portion of the stack chamber being imperforate and constituting at least about one-fourth the total height of the tapered stack. The air tends to expand as it rises, producing a pressure differential which causes air to flow into the stack assembly from the surrounding chamber 25 through the louvers 62. Thus, the air'and hot gases from the burner 7 are thoroughly mixed inthe air passages 36, 37 which surround the spreader assembly 11 and issue from the top opening 13 of the heater at a substantially uniform temperature.

The device thus functions more efliciently than a heater which discharges air heated to diflerent temperatures. Furthermore, the uniform heating and the openings provided by the louvers produce a high flow rate through the casing with attendant benefits such as long life and improved safety stemming from operation at generally lowered temperatures.

The present invention thus provides a simple and efficient device for heating and circulating air in an enclosed space or chamber. The several components are readily fabricated from sheet metal using conventional bending and cutting machines without the need for costly dies and tool work. The casing, stack and spreader of the present invention can be used with various types of burners although the type shown having a cylindrical combustion tube with an upwardly directed discharge end through which a torch flame is projected is to be preferred.

In accordance with the provisions of the patent statutes, the principles of the present invention may be utilized in various ways, numerous modifications and alterations being contemplated, substitution of parts and changes in construction being resorted to as desired, it being understood that the embodiment shown in the drawing and illustrated above is given merely for purposes of explanation and illustration without intending to limit the scope of the claims to the specific details disclosed.

What we claim and desire to secure by patent is:

1. An air heater comprising a casing enclosing an air space and having top exit and bottom entrance openings for circulation of air through such air space, a burner at the bottom of the casing, fuel supply means connected to the burner, a baflle assembly in the casing generally above the burner to control the convective flow of air upwardly through the air space induced by heat from the burner, said assembly comprising a sheet metal tubular stack having upwardly diverging sides, the stack having a bottom end opening directly over the burner to receive hot gases therefrom, the stack dividing a portion of the air space into an internal flue passage and a surrounding air chamber, said air chamber being in communication with the bottom entrance opening and of upwardly decreasing cross section, said baffle assembly also including spreader means extending vertically and centrally through the flue passage in generally spaced relation to the stack, the efiective cross sectional area of the spreader means increasing progressively upwardly and the lower end of the spreader means being spaced directly above the burner, the upper end of the spreader means having substantially its entire periphery spaced inwardly from the stack to provide a peripheral discharge outlet between the spreader means and the stack and communicating with the exit opening of the casing, and the upper end of the stack having a portion of its periphery spaced from the casing to provide an outlet opening from the upper end of the air chamber continuous with the casing exit opening.

2. An air heater as in the preceding claim in which the cross sectional area of the flue passage in the stack in a horizontal plane adjacent the bottom end opening is a relatively small portion of the cross sectional area of the casing air space in such horizontal plane.

3. An air heater comprising a casing enclosing an air space and having top exit and bottom entrance openings for circulation of air through such air space, a burner at the bottom of the casing, fuel supply means connected to the burner. a bafile assembly in the casing generally above the burner to control the convective flow of air upwardly through the air space induced by heat from the burner, said assembly comprising a sheet metal tubular stack having upwardly diverging sides, the stack having-' a bottom end opening directly over the-burner to receive hot gases therefrom, the stack dividing a portion of the air space into an internal flue passage and a surrounding air chamber, said air chamber being in communication with the bottom entrance opening and of upwardly decreasing cross section, said baflie assembly also including spreader means extending vertically and centrally through the flue passage in generally spaced relation to the stack, the effective cross sectional area of the spreader means increasing progressively upwardly and the lower end of the spreader means being spaced directly above the burner, and the stack being formed with a multiplicity of vertically spaced openings for the flow of air in separate streams between the air chamber surrounding the stack and the internal flue passage.

4. An air heater as in the preceding claim in which the stack is formed with horizontally extending louvers providing said vertically spaced openings.

5. An air heater as in claim 1 in which the stack comprises a pair of identical sheet metal companion elements each having angularly disposed integral planar panels, corresponding panels of the stack elements being disposed opposite one another across the flue passage, and each of the stack elements having an integral edge flange secured to the companion element of the pair.

6. An air heater as in claim 5 in which the planar panels of the stack elements are formed with parallel integral louvers providing a multiplicity of vertically spaced openings for the flow of air in separate streams between the air chamber surrounding the stack and the internal flue passage.

7. An air heater comprising a casing enclosing an air space and having top exit and bottom entrance openings for circulation of air through such air space, 'a burner at the bottom of the casing, fuel supply means connected to the burner, a baifle assembly in the casing generally above the burner to control the convective flow of air upwardly through the air space induced by heat from the burner, said assembly comprising a sheet metal tubular stack, the stack having a bottom end opening directly over the burner to receive hot gases therefrom, the stack dividing a portion of the airspace into an internal flue passage and a surrounding air chamber, said air chamber being in communication with the bottom entrance opening, the stack comprising a pair of identical sheet metal companion elements each having angularly disposed integral planar panels, corresponding panels of the stack elements being disposed opposite one another across the flue passage, said baflle assembly also including spreader means extending vertically through the flue passage and comprising a pair of identical sheet metal companion elements having integral flanges projecting outwardly, and the outer edges of the spreader element flanges being locatingly received in the angles between the panels of the stack elements whereby the spreader flanges constitute spacers positioning the spreader means in predetermined location within and generally separated from the stack panels for the flow of air between the stack and the spreader means.

8. An air heater as in claim 7 in which the stack elements and the spreader elements are formed with horizontally aligned openings and a rod extends through such openings interlocking the stack and the spreader means against relative vertical movement.

9. An air heater as in claim 1 in which the stack comprises a plurality of upright planar sheet metal panels, at least some of which are tapered in Width, and which are joined along adjacent edges to form a structure of rectangular section in which adjoining panels are 'angularly disposed and form opposite corners that converge downwardly, the spreader means comprising a plurality of upright planar sheet metal panels at least some of which adjoining panels are angularly disposed, said spreader structure including flanges projecting outwardly from its edge joints and received in the corner angles between the panels of the stack structure, and said spreader flanges wedging in the corners of the stack structure to support and locate the spreader structure in predetermined position within the stack both vertically and horizontally with the spreader panels confronting the stack panels in generally spaced relationfor the flow of air therebetween.

10. An air heater as in claim 9 in which the planar stack panels are formed with parallel integral louvers providing a multiplicity of vertically spaced openings for the flow of air in separate streams between the air chamber surrounding the stack and the internal flue passage.

11. An air heater as in claim 1 in which the stack is bolted to and wholly supported by the casing for facile removal and replacement and the spreader means is interlocked with and wholly supported by the stack so that the spreader means and the stack are removable from the casing as a unit upon unbolting the stack.

References Cited in the file of this patent UNITED STATES PATENTS 1,259,985 Holmes et al Mar. 19, 1918 1,502,200 Hewlett et al July 22, 1924 1,871,574 Wood Aug. 16, 1932 2,017,238 Finley Oct. 15, 1935 

